Just started using the heater for the first time the last week or so. Works fine.
I would be a little disappointed too, if my dealer said low coolant or a heater core were the problem. Both seem extremely unlikely. Hot coolant goes to the core and comes back to the engine even on modern hi-tech vehicles. If both hoses on the firewall are hot, then the heater core is also hot. If neither is hot, then a shutoff valve is not being activated as it should. If one is hot and the other not, then you may have a problem with the core. I think I read that the 3.0 has a two-stage process of moving the coolant around in order to speed the warm-up process. I suppose that's a possible participant in the problem, but doesn't seem likely.
My guess would be the core is ok. You didn't say, but I'm assuming your blower is moving vented or AC air through the vents ok and you're just not getting heated air. If that's the case, either a valve is not being commanded to open the heater coolant line, or, more likely the core is hot but the flapper valves controlling air flow through the air box (where the hot and cold air mix) are not opening. That's all done electronically through stepper motors, I think, so the problem could be as simple as a bad connection. Then again, it could be a bad switch, faulty control motor, BCM issue, pinched wire, or some such. Be glad it's under warranty and not your problem. I know, easy for me to say. Leave it to the dealer. I'm sure they'll eventually figure it out.
